My fondant recipe can be stored at room temperature for a least a month. It should be wrapped 2-3 times in plastic wrap and then placed in an airtight container. I like to use plastic tubs, but zipper bags will work as well.

As for freezing and thawing, this stuff is great. It will be good for at least a year with multiple freezings and thawings. Just let it come to room temperature on its own (don't nuke it). Getting it out the night before works really well.

I honestly don't know about a cake covered in fondant being frozen and then thawed. I've never done it. Maybe someone else here on CC would have a better answer for you.